This invention relates to the reclamation of thermoplastic scrap material such as cut film, fabric or yarn, etc., and more particularly to an apparatus and method for feeding the scrap material to and through a screw compactor for further processing the scrap material.
In the manufacture of extruded-shaped structures such as fibers and films, as well as molded objects from thermoplastic resins, a substantial amount of thermoplastic scrap material is produced. In order to effect acceptable economics in manufacture it is necessary to convert the scrap material into a form in which it can be reused.
One way of doing this is described in U.S. Pat. No. 3,193,601 which briefly stated discloses the steps of (1) continuously passing a composite mass of variable low bulk density, comprising essentially particulate thermoplastic resin through a tapered screw compactor, said compactor being driven through a preselected controlled torque to place the compacted mass of particulate thermoplastic resin issuing from said compactor under a constant pressure within the range of from 75 pounds per square inch (p.s.i.) to just below the pressure at which said compacted material would be converted into melt form, (2) continuously advancing said compacted material issuing under said constant pressure from said compactor directly into an extruder, (3) heating said mass in said extruder to a temperature effective to convert the thermoplastic resin to the molten state, and (4) thereafter continuously extruding the molten resin through extrusion dies. Preferably the extrudate is subsequently cut into particles or pellets of uniform dimension, the mass of said pellets having a uniform bulk density substantially higher than the bulk density of the mass of particulate thermoplastic resin material fed to the compactor.
This method and apparatus as well as other methods and apparatus such as that described in U.S. Pat. No. 3,389,203 are useful in converting scrap thermoplastic material into discrete particles of a form which can be readily reused. However, when attempts are made to increase the productivity of such processes, difficulties in feeding and controlling the degree and uniformity of compaction are encountered.